The dissolving metal reduction reaction, also known as a Birch reduction, is used for reducing compounds, including the reduction of aromatic compounds to 1,3-cyclohexadiene or 1,4-cyclohexadiene and dehalogenation reactions, is well known in the art. Dissolving metal reductions are an important organic synthesis tool. Although run under severe reaction conditions, the reduction has been widely applied in organic synthesis, for example in the partial reduction of an aromatic ring to 1,4-cyclohexadienes or 1,3-cyclohexadienes. Dissolving metal reductions also reduce other functional groups on an aromatic ring or olefin, including the C—X bond, wherein X is a halogen, to C—H.
The dissolving metal reduction comprises reacting with an alkali metal in the presence of a nitrogen containing base, typically ammonia. The alkali metal is typically Li, Na, K or Ca. The reaction takes place in a solvent system, for example alcohols and mixtures thereof. The dissolving metal reduction is typically carried out at a reduced temperature.
Unfortunately, a conventional dissolving metal reduction results not only in reduction of aromatic rings, but also halogens and other reducible functional groups present. Protection of the C—X bond on the halogenated aromatic ring under dissolving metal reduction conditions has not previously been shown. Selective C—X bond retention would greatly broaden the scope of the dissolving metal reduction reaction. It is therefore desirable to provide a method for selectively reducing or dehalogenating an aromatic compound.